Hello.

OPC UA defines a way to read/write/subscribe just part of an array (and the part can be a single element). You can do it with QuickOPC. An example of it is here: opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...ments%20from%20an%20array.html . In order for this to work, the server has to support it. Most servers do, but not all.

There is also a possibility that besides a node (variable) which holds the array, the server exposes separate nodes (variables) for the individual array elements. And yes, there needs to be some syntax or rule for how the Node ID looks like, depending on an index. This approach is not standardized by the OPC UA specifications, and therefore each server can do it differently. You need to consult the server vendor/documentation on this topic.

Best regards